A telecommunications system can include a distributed antenna system (“DAS”) or a repeater that can be used to extend the coverage of a cellular communication system. For example, a DAS can extend coverage to areas of traditionally low signal coverage within buildings, tunnels, or in areas obstructed by terrain features. A DAS can include one or more master units in communication with carrier systems, such as base transceiver stations of cellular service providers. The DAS can also include remote units physically separated from the master unit, but in communication with the master unit via a serial link that may be copper, optical, or other suitable communication medium.
The remote units can wirelessly communicate with user devices positioned in a coverage area. For example, the remote units can be positioned in a building, tunnel, or other structure that prevents or limits communications directly with the carriers. Remote units amplify downlink signals received from the base station via a master unit and radiate the downlink signal using an antenna. An antenna unit recovers uplink signals from mobile user equipment and provides the uplink signals to the master unit. The uplink signals can be summed together and provided back to the base station.
A remote unit can include at least one duplexer. The duplexer can isolate a transmitter output from a receiver input by allowing frequencies within the downlink band to be provided from the transmitter output to the antenna and allowing frequencies within the uplink band to be provided from the antenna output to the receiver. But, duplexers can provide little or no flexibility to respond to changes in frequency band allocation.